1. Field of the Invention
This invention relates to a process for controlling the breaking of oil-in-water emulsions induced by organic breakers.
2. Discussion of Related Art
Oil-in-water emulsion of the type commonly used in the machining of metals, such as for example cooling and lubricating, drawing, cutting or drilling emulsions, of which the oil phase consists predominantly of natural or synthetic oils of different chemical composition and origin, not only undergo wear in use, but are also contaminated through the introduction of foreign substances. Accordingly, they have to be disposed of at regular intervals. The most important step in the--in some cases continues--disposal process is the breaking of the spent emulsions, in which as much as possible of the oil phase has to be separated from the water phase in order to be able either to work up and reuse the oil phase separated off or to be able to subject the oil phase separated off together with the water phase likewise separated off to any of the usual ecologically safe disposal processes.
The orginally used method of breaking emulsions of this type by addition of mineral salts or acids has been replaced to an increasing extent, due to its ecological disadvantages and the large amount of breaker required for complete breaking, by a breaking process in which organic breakers, generally surface-active substances, are used for breaking emulsions. The advantages of this process is that the breaker concentrations required for complete breaking are very low, for example of the order of 0.1 to 10% of the quantity of emulsion, and the breakers do not interfere with disposal of the oil phase, for example by burning. In addition, they do not cause significant pollution of the aqueous phase through the introduction of foreign substances.
The disadvantages in practical terms of using organic breakers for breaking emulsions is that overdosage of the breakers used can result in re-emulsification of the already broken emulsion. The result of this is that complete breaking of emulsions is only possible in a relatively narrow dosage range of the breakers. Below this range, breaking is incomplete, which is reflected in an undesirably high oil content in the aqueous phase. Above this range, overdosage of the breaker and the resulting reemulsification likewise lead to an increase in the oil content of the aqueous phase which, of course, is also undesirable. An additional difficulty is that the oil-in-water emulsions accumulating in practice are subject to considerable variations with respect to composition, concentration of the constituents, pH value, temperature, and other parameters. The effect of these disadvantages is that, in the practical application of surface-active substances as emulsion breakers, constant trail-and-error testing of the type and quantity of breaker is necessary to determine the optimal dosage range for the organic breaker for each particular problem.
In practice, the optimal dosage range is normally determined by visual observation of breaking behavior during the emulsion breaking process. This method of determining the optical dosage range for the breaker, i.e. the end point for the addition of the surface-active compound used as breaker, is generally carried out by adding breaker until a floating oil/sludge floc is formed. To avoid overdosages, this has to be done by adding very small quantities of breaker, which explains why the breaking of oil-in-water emulsions for visual observation of the end point takes several hours to complete.
In addition, in view of increasing efforts to automate processes of this type in the field of effluent purification, there is an increasing demand for low-maintenance, reliable automatic measuring processes.
This demand cannot be satisfied even by the conventional methods known in the prior art for measuring turbidity which have been experimentally used to control the breaking of emulsions. The impurities present in spend cooling and lubrication, deep-drawing, cutting and drilling emulsions, apart from the other adverse conditions prevailing in those emulsions, lead to incorrect measurements of a magnitude which is unacceptable in practice. In particular, discoloration caused by the oils and relatively large emulsifier-demulsifier aggregates in the aqueous phase repeatedly lead to disturbance of the measurement. Practicable processes for determining the optimal dosage range for organic breakers which give reproducible results in a short time, have not been described hitherto.